distorted sounds, windows distorts, my interface does not

Here's my on-going problem. I have a MOTU interface thru which i plug in my microphones and use the program nuendo, an audio capturing program, everything sounds great. but for some reason, now that the MOTU works perfect with nuendo, all the media player sounds that microsoft has built in are distorting. if i play a song in media player it distorts. if i pull the song into nuendo it doesnt distort. if i get a windows error message, the sound will distort. here's one last thing, if the song i made using nuendo is burned onto a cd it sounds alright in a car, but not when played thru media player or some other software programs. any help would be greatly appreciated. i have bought new sound cards that are compatible with windows and MOTU. drivers are updated and all that good stuff. i had one guy pull it into his studio and it worked alright when he made a change on the MOTU, i did the same thing and no luck. any suggestions would be great. thanks